There is known to be an internal combustion engine which is capable of executing a reduced-cylinder operation where at least one of an intake valve and an exhaust valve for each cylinder of a part of plural cylinders is closed and thereby the part of plural cylinders are halted and the rest of cylinders are operated. It is known that the reduced-cylinder operation is effective to improve fuel consumption by reducing intake resistance. However, the execution of reduced-cylinder operation is sometimes restricted in various situations.
For example, there is known to be a control device that prohibits the reduced-cylinder operation which accompanies reduction of negative pressure of a surge tank in a case that evaporative fuel is purged to an intake system from a canister housing the evaporative fuel or in a case that negative pressure of a brake booster is reduced (Patent Literature #1). Further, there is also known to be a control device that sets waiting time for execution of the reduced-cylinder operation based on an engine water temperature at the moment an internal combustion engine starts up, the waiting time being required for increasing an oil temperature to a degree that the viscosity of oil decreases sufficiently, the oil being used for driving a cylinder halt system to be used for the execution of the reduced-cylinder operation (Patent Literature #2). In addition, there is known to be Patent Literatures #3 and #4 as prior art literatures relating to the present invention.